The Mineralization Features, Mechanism And Metallogenic Regularity Of The Fengtai Pb-Zn Polymetallic Ore Cluster In West Qinling, China

In recent years, owe to the development of metallogenic theory and the break through of the prospecting work, the Qinling polymetallic metallogenic belt have long been popular with many researches. A lot of new metallogenic theory have been proposed, promoting the next round of prospecting work. The west Qinling is an important origin of Pb-Zn resources in China, abundant of Pb-Zn deposit is hosted within the sediments and epimetamorphic rocks in this area. For example, many giant-large Pb-Zn deposits are hosted in the Fengxian-Taibai ("Fengtai" for short) ore cluster and the Xihe-Chengxian ("Xicheng" for short) ore cluster. Although a lot of prospecting and research works on these ore clusters have been done, the metallogenic age, the metallogenic mechanism and many other scientific problems are needed to be solved. This paper aims to describe the geological characteristics of the typical deposits in detail and do further studies of the characteristics, source and evolution of the ore-forming fluids, and the mineralization time of the ore cluster. Focused on those scientific issues,we got some main understanding as follows:1) The occurrence of the ore of the Fengtai ore cluster is controlled by the structural expanding space. The intensive structural deformation controls the lage-scale mineralization.2) The mixing of organic containing metamorphic fluid (or basinal brine) with moderate-low temperature and magmatic fluid with high temperature caused fluid immiscibility, which may have caused releasing of a large amount of CO2and/or hydrocarbons, that may be responsible for the mineralization.3) Both the base metal and sulfur are derived from the mixture of the basement rocks, the hosting Devonian strata and the Triassic magma. The regional strata was heat by the intensive magmatic activities during the Triassic, causing high-temperature regional metamorphism. As a result, a large amount of Pb and Zn loss from the regional strata formed metal-rich fluid, which tends to transform to low-temperature and low pressure area.4) The Rb-Sr dating of sulfide constraints the ages of the mineralization of the Dongtangzi Pb-Zn deposit, the Yindongshan Pb-Zn deposit and the Pb-Zn orebody of Chaima Au deposit are211.6±2.6Ma,215.3±3.2Ma and210.8±2.4Ma, respecitively, moreover, the polymetallic mineralization of the Fengtai ore cluster is spatially temporally and coupled to the regional tectonic activities.5) The tectono-magmatic mineralization of the Fengtai ore cluster has undergone multistage evolution. Different ore-forming stages may have different provenance and minerals. The copper and gold mineralization may be a bit later than lead-zinc mineralization.6) The genetic type of the Pb-Zn polymetallic deposits of the Fengtai ore cluster is clearly epigenetic, however, different from the typical MVT deposit and the Cordilleran vein-type deposits. The mineralization of the Fengtai ore cluster maybe related to the intensive magmatic activities, which heat the regional strata and provided partial ore-forming material. However, the metal and sulfur may be mainly derived from basement rocks or hosting rocks. The Pb-Zn polymetallic deposits of the Fengtai ore cluster are special epigenetic deposit in genetic type, which can be referred as a genetic type separately.7) The Pb-Zn polymetallic deposits of the Fengtai ore cluster were the product of multi-stage epigenetic hydrothermal mineralization, driven by the late Triassic regional tectono-magmatic activities of South Qinling collisional orogen of the east Paleo-Tethys tectonic domain.